Heat treatment of strip material



Nov. 22, 1966 J. B. INGALL 3,287,177

HEAT TREATMENT OF STRIP MATERIAL Filed Oct. '7, 1963 4 Sheets-Sheet 1 NVENTOR J 5. Inga Nov. 22, 1966 J. B. INGALL 3,287,177

HEAT TREATMENT OF STRIP MATERIAL Filed Oct. 7, 1963 4 Sheets-Sheet 2 INVENTQR J 5. Inga/I ATTOR NEY.

Nov. 22, 1966 J. B. INGALL 3,287,177

HEAT TREATMENT OF STRIP MATERIAL Filed Oct. 7, 1965 4 Sheets-Sheet 5 lNvEN-roR ATTORNEY J. B. INGALL HEAT TREATMENT OF STRIP MATERIAL 4 Sheets-Sheet 4 Filed 001:. 7, 1963 lNvENroR BY J 5. [21 a United States Patent 3,287,177 HEAT TREATMENT OF STRIP MATERIAL James Birkett Ingall, Sutton Coldfield, England, assignor to Birlec-Efco (Melting) Limited Filed Oct. 7, 1963, Ser. No. 314,405 13 Claims. (Cl. 14813) This invention relates to the continuous heat treatment of elongate metal material, such as the continuous annealing of steel strip.

According to the present invention in one aspect, there is provided a method for the continuous heat treatment of elongate metal material, which comprises passing the material longitudinally through a bath of fluid heat transfer medium, heating the fluid to heat the material in turn by thermal conduction in an intermediate portion of the materials path through the bath, and circulating the fluid in the remaining portions of the bath to transfer heat from the outgoing material to the ingoing material.

In another aspect the present invention contemplates improved heat treatment apparatus for carrying out such method.

The fluid medium through which the material is passed may be a liquid so that it is capable of being subjected to a pumping action, or it may be a fluidised medium.

It is advantageous for the fluid medium to be electrically conductive, since in this event the said intermediate portion which is heated can be formed as part of a closed loop to act as a secondary winding in a transformer heating arrangement.

If the fluid medium is not electrically conductive, a transformer heating arrangement may still be employed in which a closed loop of fluid medium is provided, as above, and the walls of the container for such loop act as secondary winding. In this case the walls of the looped container are inductively heated, and the heat is conducted to the liquid, and thence to the material passing therethrough.

In order that the present invention may be clearly understood the same will now be more fully described, by Way of example, with reference to the accompanying drawings, in which:

FIGURE 1 illustrates diagrammatically one form of apparatus according to the invention, and

FIGURE 2 illustrates a preferred form of such apparatus.

Referring to FIGURE 1, a generally U-shaped chamber 11 is provided at its bight 12 with guiding means in the form of a roller 13 for strip 14. The strip 14 enters the chamber 11 down the left-hand limb thereof and emerges from the right-hand limb as indicated by arrows on the strip. -The limbs of chamber 11 are joined by transverse passageways 15 and 16, passageway 15 being remote from the bight 12 while the passageway 16 is nearer the bight. Also, passageway 16 is of greater cross-sectional area than that of passageway 15, which latter passageway is shown as containing a pump 17 for circulating a fluid heat transfer medium contained in the chamber, the upper level of which medium is shown as being located above the passageway 15.

The bight 12 and adjacent limb portions of chamber 11 form a loop together with passageway 16, which loop is embraced by a laminated core 18 of a transformer the primary winding of which is represented at 19 and is connected to a suitable alternating voltage supply source 20.

The fluid heat transfer medium through which strip 14 is passed is preferably electrically conductive, and a suitable material for this purpose is an alloy of lead such as lead/ bismuth eutectic.

If an electrically conductive fluid medium is used the loop of fluid referred to above, and identified as CEGF,

3,287,177 Patented Nov. 22, 1966 forms a single turn secondary winding of low impedance for primary winding 19 and core 18. The fluid in the loop is accordingly heated and this heat is transferred, conductively, to strip 14 passing through the bight 12. If the fluid medium is not electrically conductive, the walls of the chamber forming the loop act as a secondary turn and these are heated, the heat being conducted from the walls to the fluid and, in turn, from the fluid to the strip. The strip is accordingly heated, in either event, to the maximum temperature in the desired heat treatment as it passes through the bight 12, and in the case of annealing ferrous strip material this will be an annealing temperature of the order of 700 C., or higher.

As the heated strip leaves the bight 12 it enters the righthand limb portion D and is quenched by the fluid therein which fluid is itself accordingly heated. The fluid in the right-hand limb is circulated to the left-hand limb by the action of pump 17, so that ingoing strip passing through limb portion B is preheated and the fluid therein is cooled before returning to limb portion D again. This heat transfer cycle increases the thermal efi'lciency of the process by transferring heat from outgoing strip to ingoing strip, and this efficiency is additionally improved by the action of pump 17 in circulating liquid around the closed loop indicated as ABCD as shown by the broken line arrows to be in contraflow with the strip in limb portions B and D.

In the case of annealing the strip may be preheated to a temperature of the order of 200 C. by the above arrangement and operation before entering the bight portion.

The practical advantage of the above arrangement stems from the fact that the fluid medium in the bight portion, which fluid is heated to heat the strip to the maximum temperature during treatment, remain relatively static and the maximum temperature is thus more readily controlled. Any movement of fluid which does occur in the bight portion will tend to follow the strip and then be circulated through passageway 16 whereafter it will be at least partially drawn once more into the =bight portion again with the strip movement. Thus any fluid movement in the bight portion will largely tend to form a closed loop recirculation maintaining fluid at high temperature in the bight portion. Considering then the theoretical ideal with the present arrangement and operation, the only heat input required is that necessary to heat the strip from entry or room temperature to the preheat or rather exit temperature, these being substantially equal, since additional heat required to raise the strip to maximum temperature is subsequently recovered; and the maximum temperature itself is readily controlled since it is effectively equal to that of the substantially static, but slightly recirculating, fluid in the bight portion.

FIGURE 2 illustrates a modified form of the arrangement of FIGURE 1 which modified form employs a straight duct 30 for passage of strip therethrough instead of a U-shaped chamber. A central portion 30a of duct 30 is bypassed by a pipe 31 and the ends of duct 30 are connected by -a pipe 32. The duct 30 and pipes 31, 32 are filled wih liquid heat transfer medium which is circulated by electromagnetic pumps 33, 34 individually associated with pipes 31, 32. In operation, pumps 31, 32 are arranged to pump at equal rates whereby fluid circulates from one end of duct 30, through pipe 31, to the other end of duct 30, and through pipe 32, as indicated :by broken-line arrows. It will be understood that with such operation, fluid in the central duct portion 30a remains relatively static.

The central duct portion 3011 has three W-shaped fluid channels 35 depending therefrom, each such channel having a heating transformer core 36 located around its central arm. Thus each channel 35 forms, with the respective bridging part of duct portion 30a, two closed loops having a common arm and the fluid in which can be regarded as forming a two-turn secondary winding for the guide rollers 41, 42.

The fluid medium will normally be maintained under a controlled protective atmosphere where appropriate, such as by use of covers 43, 44 for chambers 41, 42 with suitable strip inlet and outlet seals indicated at 45, 46. This use of a protective atmosphere is particularly important where the liquid medium is a metal subject to undesirable contamination by contact with air, and this is equally applicable to the arrangement of FIGURE '1.

The operation is similar to that of FIGURE 1 described above, with the strip and fluid medium moving in contraflow. However, the arrangement of FIGURE 2 afiords various advantages of that of FIGURE 1 in that the duct 30 is of flat form and no guide rollers are required in the higher temperature zones where sealing difliculties and undesirable marking of, the strip by a' roller can arise.

Also in the arrangement of FIGURE 2 channels 35 are specially provided to form part of the heating transformers secondary windings. The provision of a number of such transformers and channels is itself advantageous in allowing the input heating load to be spread out in association with a greater length of duct 30, and in the present example of three transformers a balanced threephase arrangement may be employed.

At the same time the special provision ofchannels 35 and the separate. provision of bypass pipe 31 means that no part of the contrafiow liquid medium circuit forms part of the transformer heating circuits and the fluid in bypass pipe 31 can be individually pumped. Thus, heat input is concentrated in fluid medium which is subject to little or no motive force other than the drag from the strip and circulated fluid.

Other advantages of the arrangement of FIGURE 2 are as with FIGURE 1, and in partciular the facilitation of controlling the maximum treatment temperature which is found in relatively static fluid medium. Temperature measuring means are indicated symbolically at 47, al-

though in practice these means may be of radiation pyrometer or other suitable form.

I claim:

1. A method for the continuous heat treatment of elongate metal material, which comprises the steps of passing the material longitudinally through a bath of fluid heat transfer medium, heating the fluid to heat the ma- .terial in turn by thermal conduction in an intermediate tion, the direction of circulation through said remaining portions being opposite to that in which said material travels.

3. A method according to claim 1 wherein the fluid .medium is electrically conductive, and which comprises the step of causing part of the fluid in said bath to flow in a second c uit, part of which second circuit is concurrent with said intermediate bath portion, and employ ing said second circuit as a secondary winding in an inductive heating arrangement.

4. A method according to claim 3 wherein the first mentioned circuit bypasses said intermediate portion in-- depently of said second circuit.

5. A method for the continuous annealing of ferrous strip, which comprises the steps of passing the strip 1011- gitudinally through a bath of electrically conductive liquid heat transfer medium, the liquid bath being formed by two separate portions of a first liquid circuit which por- -tions are bridged by part of a second liquid circuit; em-- ploying said second liquid circuit as a secondary winding circuit for an inductive heating arrangement to heat the liquid therein to annealing temperature and to heat to. such temperature, in turn the strip passing therethrough by conduction from the liquid; and circulating the liquid in an intermediate portion of the bath, and means for.

circulating fluid in 5 the-remaining portions of the bath from the portion last encountered by the metal material to the portion thereof first encountered thereby so as to transfer. heat from the outgoing material to the ingoing material. 7 a

7. Apparatus according to claim 6 comprising first fluid transfer means connecting the ends of said bath, and

second fluid transfer means connecting said remaining bath portions to by-pass said intermediate bath portion nearer said intermediate portion, whereby said transfer.

means and said remaining bath portions form a circuit for fluid circulation, and wherein the fluid circulating means comprises pump means associated with said first fluid transfer means.

8. Apparatus according to claim 7 wherein the said.

second fluid transfer means and said intermediate bath portion form a second circuit for fluid circulation and fluid heating means comprises a transformer heating arrangement including a core located around said second circuit, at least one of said second circuit and the fluid therein being electrically conductive so as to serve as a secondary Winding circuit for the transformer arrangement.

9. Apparatus for the continuous heat treatment of elongate metal material comprising a U-shaped duct for fluid heat transfer medium, means for passing the material longitudinally through said duct, a first fluid passageway interconnecting the limbs of said duct towards the outer ends thereof, a second fluid passageway interconnecting the limbs of said duct towardsthe bight thereof, means -for heating fluid in the bight of said duct, and means for circulating fiuid around the fluid circuit formed by said. fluid passageways and the duct limb portions bridging corresponding ends of said passageways.

10. Apparatus according to claim 9 wherein the heating means comprises a transformer heating arrangement including a core located around the bight of said duct, said bight and second passageway forming a second circuit for circulation of said fluid and at least one of said second.

circuit and the fluid therein being electrically conductive and acting as secondary winding circuit for the transformer arrangement.

11. Apparatus for the continuous heat treatment of elongate metal material, comprising a substantially horiportion, and means associated with both said transfer means for circulating fluid around the fluid path formed by said transfer means and the portions of said duct bridging corresponding ends thereof, the fluid circulating means :being operable to circulate fluid through said bridging duct portions in a direction opposite to that in which said material passes.

12. Apparatus according to claim 11 comprising fluid container means depending from and in communication with at least part of said intermediate duct portion to form therewith a second fluid circuit, and wherein said heating means comprises a heating transformer arrangement including a core located around part of said container, at least one of said second circuit and the fluid therein References Cited by the Examiner UNITED STATES PATENTS 2/1962 Beggs et al. 148-13 5/11962 Cook et al. l48l3 6/1965 Inoue 14820.6

DAVID L. RECK, Primary Examiner.

being electrically conductive and acting as a secondary 15 R. O. DEAN, Assistant Examiner.

winding circuit for the transformer arrangement. 

1. A METHOD FOR THE CONTINUOUS HEAT TREATMENT OF ELONGATE METAL MATERIAL, WHICH COMPRISES THE STEPS OF PASSING THE MATERIAL LONGITUDINALLY THROUGH A BATH OF FLUID HEAT TRANSFER MEDIUM, HEATING THE FLUID TO HEAT THE MATERIAL IN TURN BY THERMAL CONDUCTION IN AN INTERMEDIATE PORTION OF THE MATERIALS PATH THROUGH THE BATH, AND CIRCULATING THE FLUID IN THE REMAINING PORTIONS OF THE BATH FROM THE PORTION OF THE BATH LAST ENCOUNTERED BY THE MATERIAL TO THE PORTION THEREOF FIRST ENCOUNTERED THEREBY TO TRANSFER HEAT FROM THE OUTGOING MATERIAL TO THE INGOING MATERIAL. 